The present invention is directed toward a prosthetic joint, and more specifically, toward a prosthetic joint that can be configured as either a single- or double-axis joint.
The joints of a human body are subject to substantial stresses, and as people age, their joints often function less effectively than when they were younger. Injury and disease can also affect joint function. It is becoming increasingly common to replace natural joints in the human body with artificial ones when the natural joints wear out or no longer function properly. Artificial hips and knees are widely used, and other joints such as the elbow are also replaced on occasion.
Most artificial joints include a stem or anchor portion that is inserted into the bone on either side of the damaged joint and a pair of bearing surfaces at the protruding ends of the stems that interact with one another to form a joint. Various joints in the body are generally replaced with structurally similar artificial joints; thus a knee joint will generally be replaced with a hinge joint and a hip joint will be replaced with a ball-and-socket joint. In some cases, however, such as with elbow joints, it may be desirable to replace the natural joint with an artificial joint structurally different from the original joint to improve the function of the patient""s joint. Thus a natural single-axis elbow joint is sometimes replaced with a prosthetic device that includes two pivotal axes. In this case, a stem embedded in an ulna connects to a central joint element at a first location and a stem embedded in a humerus connects to the central joint element at a second location spaced apart from the first location so that both posts pivot about different, normally parallel, axes. Such bi-axial elbow joints and the benefits and uses thereof are described in greater detail in U.S. Pat. Nos. 5,314,484 and 5,376,121 which patents are hereby incorporated by reference.
The type of replacement joint selected by a surgeon will depend on many factors including the age, health and activity level of the patient and the size and condition of the bones adjacent the joint being replaced. Unfortunately, it is often difficult to determine which of these joint types should be used until a patient""s joint has been exposed during surgery. This is especially true in elbow replacement surgery where a the need for a double axis joint is often not evident until the damaged joint can be directly examined. Thus, a surgeon may need to obtain both types of joints prior to a surgery even though only one joint will be used. Because double-axis elbows are used less frequently that single-axis joints, and are also more expensive than single-axis joints, surgeons may tend to use a single-axis joint even in cases where a double-axis joint would be more appropriate. Moreover, because a surgeon may need to partially install or modify one of the artificial joints before determining that a different device would be preferable, it may be necessary to discard one of the two prostheses at a considerable cost.
It is known to provide certain types of prosthetic joints in kit form which kits include a plurality of different elements, some or all of which may be used to form a given joint depending on the condition of the natural joint as revealed by surgery. For example, U.S. Pat. No. 6,027,534 describes a modular elbow kit that includes three different bearing elements. A first element is used when the elbow joint is to be configured in a constrained mode and a second and third element are used instead of the first element when the joint is to function in an unconstrained mode. Beneficially, the same kit can be used in a wide variety of patients. Stocking identical kits is generally less expensive that stocking a variety of different prosthetics, and, as a majority of the items in each kit will be used in every surgery, waste is minimized.
It would be therefore be desirable to provide a kit for forming a prosthetic joint that could be assembled to produce either a single-axis joint or a double-axis joint.
This problem is overcome by the present invention which comprises a prosthetic joint configurable as either a single-axis joint or a double-axis joint. While the subject invention could be used in various parts of the body, it finds particular utility as an elbow joint, and hereinafter, the invention will primarily be described in terms of an elbow joint, it being understood that it could also function in other locations in the body such as the knee.
In general terms, the invention comprises the provision of an adaptor for use with a single-axis joint to convert the single-axis joint to a double-axis joint when called for. The adaptor may be sold by itself or as part of a kit with the single-axis joint. An ordinary single-axis joint includes a first element insertable in a first bone, such as a humerus and a second element insertable into a second bone such as an ulna. The distal end of the humeral component and the proximal end of the ulnar component extend from the respective bones, and the distal end of the humeral element has a first shape and the proximal of the second element has a second shape complimentary to the first shape. By complimentary, it is meant that the first shape mates or fits with the second shape to form a joint. Thus a sphere and a depression would be complementary shapes (mating like a ball-and-socket joint) as would a single arm receivable between a pair of spaced-apart arms (a hinge joint). The typical joint also includes a pin or similar connector for pivotably joining the distal end of the humeral element to the proximal end of the ulnar component. To convert the single-axis joint to a double axis joint, a connector or adaptor is provided that has a first end having a shape complementary to the shape of the distal end of the humeral component and a second end having a shape complementary to the shape of the ulnar component which adaptor can thus be placed between the ends of the humeral and ulnar components and pivotally connected to each to form a double axis joint. In the preferred embodiment, the complementary shapes are described as a first end of a first element that is received between the spaced apart arms of a second element; however other complementary shapes could be used as well.
In a preferred embodiment, the invention comprises a humeral component having a stem portion for insertion into the interior of a humerus and a second end, an ulnar component having a first end for insertion into the interior of an ulna and a second end, and a connector for pivotably joining the second ends to form a joint. A first connector comprises a pin that directly connects the second ends of the components to form a single-axis joint while a second, alternate, connector comprises a spacing element that has a first portion connectable to the second end of the humeral element with a pin and a second portion connectable to the second end of the ulnar element with a pin to form a double-axis joint. The first portion of the spacing element is generally similar in shape to the second end of the ulnar element while the second portion of the spacing element is generally similar in shape to the second end of the humeral element.
The second end of the humeral element includes a pair of parallel, spaced apart arms each having a bore which bores are coaxially aligned. The second end of the ulnar element is somewhat narrower than the spacing between the arms of the humeral element and includes a bore of approximately the same diameter as the bores in the humeral element arms so that when the bore in the ulnar element is aligned with the bores in the humeral element and a pin is inserted through the aligned bore, a joint is formed. A bearing insert is also preferably used between the ulnar and humeral elements to reduce wear and keep the ulnar element properly spaced with respect to the humeral element.
The connector of the preferred embodiment is generally Y-shaped and includes two parallel arms that extend from a body portion in a first direction and a third arm that is centered between and parallel to the first and second arms but which extends from the body portion in a direction opposite to the first and second arms. To form a double-axis joint, the third arm of the connector is connected between the arms of the humeral element with a pin and the second end of the ulnar element is connected between the parallel arms of the connector with a pin to form a double-axis joint. The prosthesis is sold in kit form so that a surgeon need obtain only one kit, and the surgeon can install the joint with or without the connector depending on the condition of the natural joint as revealed by surgery.
It is therefore a primary object of the present invention to provide an artificial joint configurable as either a single-axis joint or a double-axis joint.
It is another object of the invention to provide a method of installing an artificial joint as either a single-axis joint or a double-axis joint.
It is a further object of the invention to provide an adaptor for converting a single-axis joint to a double axis joint.
It is still another object of the invention to provide a kit for assembling a prosthetic joint.
It is still a further object of the invention to provide a prosthetic joint kit that includes a first element for connection to a first bone, a second element for connection to a second bone, and two connectors, either of which can be used to pivotably connect the first and second elements.
In furtherance of the foregoing objects, a prosthetic elbow is disclosed that includes a humeral component and an ulnar component adapted to pivotably engage the humeral component and an adaptor having a first end pivotably connected to the ulnar component and a second end pivotably connected to the humeral component.
Also disclosed is a kit assembleable in a first configuration to form a single-axis prosthetic joint and in a second configuration to form a double-axis prosthetic joint that includes a first component having a proximal end insertable into a first bone and a distal end, a second component having a distal end insertable into a second bone and a proximal end, and an adaptor connectable between the first component and the second component. The kit is assembled by connecting the first component directly to the second component to form a single-axis joint or by connecting the adaptor between the first component and the second component to form a double-axis joint.
A method of assembling a prosthetic joint is also disclosed that includes the steps of providing a first joint component having a first end adapted to be inserted into the interior of a first bone and a second end, a second joint component having a first end adapted to be inserted into the interior of a second bone and a second end, a first connector for forming a single-axis pivotal connection between the first component and the second component, and a second connector for forming a double-axis pivotal connection between the first component and the second component. Then one of the first and second connectors is selected and used to connect the first component to the second component.
A double-axis prosthetic joint is also described that is formed from a first component having a proximal end adapted to be mounted in a first bone and a distal end comprising a pair of spaced apart arms and a second component having a distal end adapted to be mounted in a second bone and a proximal end including a bore. The joint also includes a connector for pivotably connecting the first component to the second component which connector has a first end having a bore which is pivotably mounted between the first component spaced apart arms and a second end comprising a pair of spaced apart arms. The second component distal end is pivotably mounted between the connector second end spaced apart arms.
Another aspect of the invention comprises a prosthetic joint kit including a first component having a first end and a second end comprising a pair of spaced apart arms and a second component having a first end and a second end comprising a bore. The kit also includes a first connector for pivotably connecting the first component directly to the second component and a second connector for pivotably connecting the first component indirectly to the second component.
Another aspect of the invention comprises a method of converting a single-axis prosthetic joint to a double-axis prosthetic joint that includes the steps of providing a first joint element having a first end insertable into a bone and a second end having a first shape, and a second joint element having a first end insertable into a bone and a second end having a second shape complementary to the first shape. The second end is pivotably connectable to the first joint second end to form a single-axis prosthetic joint. A connector is also provided that has a first end having a shape complementary to the first shape and a second end complementary to the second shape that can be used to pivotally attach the first joint element second end to the connector first end, and the second joint element second end to the connector second end to form a double-axis prosthetic joint.